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When running umount /path I get:

umount: /path: device is busy.

The filesystem is huge, so lsof +D /path is not a realistic option.

lsof /path, lsof +f -- /path, and fuser /path all return nothing. fuser -v /path gives:

                  USER        PID ACCESS COMMAND
/path:            root     kernel mount /path

which is normal for all unused mounted file systems.

umount -l and umount -f is not good enough for my situation.

How do I figure out why the kernel thinks this filesystem is busy?


I have made a page with examples of all solutions so far here: http://oletange.blogspot.com/2012/04/umount-device-is-busy-why.html

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Is your shell's current directory on the mountpoint path? –  ultrasawblade Jun 15 '11 at 11:49
No. Then fuser would say so. –  Ole Tange Jun 15 '11 at 11:58
You actually want fuser -vm /path ... –  derobert Oct 23 '12 at 17:23
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6 Answers

up vote 33 down vote accepted

It seems the cause for my issue was the nfs-kernel-server was exporting the directory. The nfs-kernel-server probably goes behind the normal open files and thus is not listed by lsof and fuser.

When I stopped the nfs-kernel-server I could umount the directory.

I have made a page with examples of all solutions so far here: http://oletange.blogspot.com/2012/04/umount-device-is-busy-why.html

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Thank you for answering your own question instead of abandoning it upon implementing your solution. Your answer helped me sort out a similarly exported NFS share. –  Jeff Welling Dec 15 '11 at 5:44
This same issue can also occur if you've set up loopback devices on the filesystem - for example if /dev/loop0 is backed by a file in /path. –  BruceCran Feb 22 '12 at 13:25
+1 for the blog link, which also saved my skin –  Mike Pennington Nov 8 '13 at 14:57
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To add to BruceCran's comment above, the cause for my manifestation of this problem just now was a stale loopback mount. I'd already checked the output of fuser -vm <mountpoint>/lsof +D <mountpoint>, mount and cat /proc/mounts, checked whether some old nfs-kernel-server was running, turned off quotas, attempted (but failed) a umount -f <mountpoint> and all but resigned myself to abandoning 924 days' uptime before finally checking the output of losetup and finding two stale configured-but-not-mounted loopbacks:

parsley:/mnt# cat /proc/mounts 
rootfs / rootfs rw 0 0
none /sys sysfs rw,nosuid,nodev,noexec 0 0
none /proc proc rw,nosuid,nodev,noexec 0 0
udev /dev tmpfs rw,size=10240k,mode=755 0 0
/dev/mapper/stuff-root / ext3 rw,errors=remount-ro,data=ordered 0 0
tmpfs /lib/init/rw tmpfs rw,nosuid,mode=755 0 0
usbfs /proc/bus/usb usbfs rw,nosuid,nodev,noexec 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
devpts /dev/pts devpts rw,nosuid,noexec,gid=5,mode=620 0 0
fusectl /sys/fs/fuse/connections fusectl rw 0 0
/dev/dm-2 /mnt/big ext3 rw,errors=remount-ro,data=ordered,jqfmt=vfsv0,usrjquota=aquota.user 0 0


parsley:/mnt# fuser -vm /mnt/big/
parsley:/mnt# lsof +D big
parsley:/mnt# umount -f /mnt/big/
umount2: Device or resource busy
umount: /mnt/big: device is busy
umount2: Device or resource busy
umount: /mnt/big: device is busy

parsley:/mnt# losetup -a    
/dev/loop0: [fd02]:59 (/mnt/big/dot-dropbox.ext2)
/dev/loop1: [fd02]:59 (/mnt/big/dot-dropbox.ext2)

parsley:/mnt# losetup -d /dev/loop0
parsley:/mnt# losetup -d /dev/loop1
parsley:/mnt# losetup -a
parsley:/mnt# umount big/

A Gentoo forum post also lists swapfiles as a potential culprit; although swapping to files is probably pretty rare these days, it can't hurt to check the output of cat /proc/swaps. I'm not sure whether quotas could ever prevent an unmount — I was clutching at straws.

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All 924 days uptime means is that you need to update your kernel patches :-) –  w00t Jun 25 '12 at 13:39
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For me, the offending process was a daemon running in a chroot. Because it was in a chroot, lsof and fuser wouldn't find it.

If you suspect you have something left running in a chroot, sudo ls -l /proc/*/root | grep chroot will find the culprit (replace "chroot" with the path to the chroot).

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Nice, and in FreeBSD I did this: sudo ls -l /proc/*/status | grep HOST where HOST is the hostname of the jail –  JGurtz Jul 24 '13 at 22:31
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Instead of using lsof to crawl through the file system, just use the total list of open files and grep it. I find this returns must faster, although it's less accurate. It should get the job done.

lsof | grep '/path'
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lsof /path looks through the path only. –  Ole Tange Jun 15 '11 at 11:58
I didn't say lsof /path, I said lsof | grep '/path'. The difference is that lsof with no arguments shows all open files using some sort of cache table, and grep is very fast at searching through it. The things you tried with lsof make it scan through the file system which takes a long time. –  Caleb Jun 15 '11 at 12:02
Like I said: lsof /path looks at the path only. It does not look at every single file. It is often much faster than lsof | grep /path (in my unscientific test it was 20 times faster YMMV) since it does not look at all open files but only the files for that path. –  Ole Tange Jun 16 '11 at 10:10
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I had this issue, and it turned out that there were active screen sessions in the background I didn't know about. I connected to the other active screen session and its shell wasn't even currently sitting in the mounted directory. Killing those other shell sessions fixed the issue for me.

Just thought I'd share my resolution.

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For fuser to report on the PIDs holding a mount open you have to use -m

fuser -m /path
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True, but irrelevant: lsof /path provides the same list of PIDs as fuser -m /path. –  Gilles Jun 16 '11 at 7:55
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